ABSTRACT In pregnancy, endothelial vasodilation is enhanced to decrease blood pressure and increase uterine blood flow. Pregnancy-enhanced vasodilatory function is achieved through an increase in expression of angiotensin type 2 receptor (AT2R) in the endothelium of uterine and systemic vasculature. In preeclampsia, this adaptive endothelial response fails due to downregulation of AT2R expression and activity, with associated endothelial dysfunction, increased vascular resistance, and hypertension. Preeclampsia affects 5%?8% of all pregnancies, and treatment is limited to antihypertensives that relax vascular smooth muscle. There is no treatment to directly address endothelial failure. The cause of preeclampsia is not known, but the pregnancy-specific upregulation of AT2R in the vasculature may hold important keys to understanding the origins of the disease and the underlying causes of maternal organ function. The opportunity to study the effects of novel oral nonpeptide Compund21 is significant and valuable. Based on solid preliminary data, we propose that pregnancy selectively upregulates endothelial AT2R via differential binding of ligand-activated estrogen receptor (ie, ER? vs ER?) to a functional estrogen response element (ERE) in the AT2R promoter. Failure of vascular AT2R upregulation during pregnancy plays a role in endothelial cell dysfunction and vasoconstriction in preeclampsia and, consequently, activation of this system reverses preeclamptic vascular dysfunction. Aim 1 will first establish pregnancy-specific upregulation of AT2R in the endothelium and then define the mechanistic role of ER ? or ? in upregulation of AT2R by using ER-specific agonists, antagonists, and siRNA in rodent models. AT2R transcription mechanisms will determine differential binding of ligand- activated ER and transcription factors to putative ERE in AT2R promoter in primary human uterine artery endothelial cells, using ChiP and EMSA/ supershift assays, and then use reporter assays to determine their functionality. Aim 2 will move towards clinical translational relevance. We will determine if vascular AT2R is involved in preeclamptic endothelial dysfunction and if AT2R activation rescues vascular dysfunction. To test the AT2R-mediated mechanisms, EDHF, NO, and PGI2 pathways of vascular relaxation pathways will be determined. Also, the expression of eNOS and its activity state?signaling components of EDHF and PGI2 pathways as well as nitrate/ nitrite and PGI2 production and changes in membrane potential?will be measured. Aim 3 will verify the AT2R effects in vivo. We will use 2 models of gestational hypertension to test the effect of 2 selective AT2R agonists (CGP-42112 peptide and Compound 21) on the maternal, placental, and fetal abnormalities associated with preeclampsia. These studies will provide new information of how pregnancy increases endothelial AT2R and that failure of this process leads to preeclamptic endothelial dysfunction. The positive translational significance of these aims is that they evaluate the therapeutic utility of an endothelium- targeted therapy which is potentially safe in preeclampsia subjects.